Dry Eye Syndrome is a disorder of the tear film resulting from tear deficiency which causes discomfort and damage to the inter-palpebral ocular surface. Tears are an extracellular fluid covering the surface epithelial cells of the corneal and conjunctival epithelium. The functions of the tear film include lubrication the surface of the eye and the eyelids, optimizing the refractive function of the anterior segment, and providing a means for removal of environmental contaminants from the ocular surface.
The normal tear film is composed of three layers: an outer lipid layer (approximately 0.1 μm thick) produced by the meibomian glands in the tarsal plate, a central aqueous layer (approximately 7-10 μm thick) produced by both the main and accessory lacrimal glands, and an inner mucin layer (approximately 0.2-1.0 μm thick) produced by goblet cells in the conjunctiva.4-8 The list of tear components includes water, electrolytes, lipids, and proteins (such as lipocalin, lactoferrin, mucins, and lysozyme), as well as various immunoglobins, growth factors and cytokines. When the quality or quantity of tears is compromised by an imbalance or breakdown in these components, it can severely impact the eye and cause or exacerbate dry eye symptoms.